Plaskon was charged with stabbing to death 16-year-old Maren Sanchez in a hallway at Jonathan Law High School in 2014. His family and friends said he was unhappy that she had declined to go to the prom with him.

The teen's defense attorney, Edward Garvin, said his client suffered from psychosis and the rejected prom invitation was not the motive for the stabbing.

But prosecutor Kevin Lawlor said several witnesses agreed the spurned invite was the cause of Plaskon's actions.

State law allows the teen to apply for parole in 13 years because Plaskon was 16 when he killed the girl, Garvin said.

"I've said it before and I've said it to countless families: No number (of years in prison) is going to bring your loved one back. I just hope they can move on and heal," the prosecutor said.

Sanchez's mother declined to comment after the hearing.

Witnesses tried to intervene in the early morning attack on Sanchez, according to an arrest warrant affidavit. Plaskon was taken to the principal's office with his clothing soaked in blood and said "I did it. Just arrest me," according to the court document.